SummaryHyphae of the dimorphic fungus, Candida albicans, exhibit directional tip responses when grown in contact with surfaces. On hard surfaces or in liquid media, the trajectory of hyphal growth is typically linear, with tip re-orientation events limited to encounters with topographical features (thigmotropism). In contrast, when grown on semisolid surfaces, the tips of C. albicans hyphae grow in an oscillatory manner to form regular two-dimensional sinusoidal curves and three-dimensional helices. We show that, like thigmotropism, initiation of directional tip oscillation in C. albicans hyphae is severely attenuated when Ca 2+ homeostasis is perturbed. Chelation of extracellular Ca 2+ or deletion of the Ca 2+ transporters that modulate cytosolic [Ca 2+ ] (Mid1, Cch1 or Pmr1) did not affect hyphal length but curve formation was severely reduced in mid1D and cch1D and abolished in pmr1D. Sinusoidal hypha morphology was altered in the mid1D, chs3D and heterozygous pmr1D/PMR1 strains. Treatments that affect cell wall integrity, changes in surface mannosylation or the provision of additional carbon sources had significant but less pronounced effects on oscillatory growth. The induction of twoand three-dimensional sinusoidal growth in wild-type C. albicans hyphae is therefore the consequence of mechanisms that involve Ca 2+ influx and signalling rather than gross changes in the cell wall architecture.
SummaryHyphal growth of Candida albicans is characterized by asymmetric cell divisions in which the subapical mother cell inherits most of the vacuolar space and becomes cell cycle arrested in G1, while the apical daughter cell acquires most of the cell cytoplasm and progresses through G1 into the next mitotic cell cycle. Consequently, branch formation in hyphal compartments is delayed until sufficient cytoplasm is synthesized to execute the G1 'START' function. To test the hypothesis that this mode of vacuole inheritance determines cell cycle progression and therefore the branching of hyphae, eight tetracycline-regulated conditional mutants were constructed that were affected at different stages of the vacuole inheritance pathway. Under repressing conditions, vac7, vac8 and fab1 mutants generated mycelial compartments with more symmetrically distributed vacuoles and increased branching frequencies. Repression of VAC1, VAM2 and VAM3 resulted in sparsely branched hyphae, with large vacuoles and enlarged hyphal compartments. Therefore, during hyphal growth of C. albicans the cell cycle, growth and branch formation can be uncoupled, resulting in the investment of cytoplasm to support hyphal extension at the expense of hyphal branching.
Pseudohyphal growth of Candida albicans has been recognized as a morphological growth form that exhibits characteristics that are distinct from those of the budding yeast phase and true hyphal form of this pathogenic fungus. In Saccharomyces cerevisiae, pseudohypha growth involves synchronous unipolar cell divisions that are a modification of the bipolar budding pattern of diploid cells. While pseudohyphae of C. albicans also exhibit unipolar cell divisions, live cell imaging demonstrated departures from the normal unipolar pattern. Buds occasionally followed a bipolar or axial budding event in which buds could be formed from the proximal or distal ends of a parent pseudohypha. This extends the known morphological repertoire of cell division patterns in C. albicans pseudohyphal cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.